To have a notify me feature once a user status changed from "in a call" to other status. .
It is hassle to keep checking on someone who is always in a call i.e management or bosses. If we missed out the opportunity then we have to wait for another time frame.
With this notification i.e tag user - notify me when he ended his call.
We can immediately keep in touch with user immediately. Else the user will have another meeting and we do not have the chance to get in touch with him/her